Correction of non-common path aberration using a deformable lens in pyramid wavefront sensor-based AO systems (Conference Presentation)

Abstract

Pyramid wavefront sensors are widely used in adaptive optics system, and in particular in extreme adaptive optics applications, due to their advantages in terms of sensitivity with respect to other wavefront sensors such as Shack Hartmann or curvature wavefront sensors. In particular, as the adaptive optics loop is closing, the reference star image size gets smaller on the pyramid tip, providing increased sensitivity. However, non common path aberrations are usually present due to light splitting between wavefront sensor and scientific optical beams, because of the presence of different optical elements. This causes image distortions that can hinder the scientific throughput and are then usually corrected by introducing offsets on the pyramid closed loop control systems. This increases the size of the star image at the pyramid tip, leading to a decrease in sensitivity that compromises the aforementioned advantages. In this work we aim at correcting the non common path aberrations by inserting a multi actuator deformable lens in the sensing path to recover the optimal working conditions and the ideal gain. In particular, we aim at demonstrating that it is possible to insert the multi actuator deformable lens in the sensing arm and drive it while the main adaptive optics loop is working, maximizing the scientific image sharpness. The use of this lens avoids changes in the optical configuration, providing a simple, yet effective way to correct for non common path aberrations in existing setups.